Is zakat due on a share in a failing company whose value has not been paid, and is zakat due on installments as soon as they are received?

"Neither the partner nor the mudarib (investing partner) guarantees the capital of his partner unless there is transgression or negligence on his part, because he is an entrusted party. Losses in a partnership are distributed according to the capital contribution of each partner. If your share in the company reaches the nisab and a year has passed over it (hawl), then zakat becomes obligatory on it. However, if your share is a debt owed by your partner due to his transgression, then it is subject to zakat on debts. If the debtor is solvent, its owner should pay zakat on it for each year. If the debtor is insolvent or procrastinating, it is more prudent to pay zakat on it upon its retrieval."